This application claims the benefit of United Kingdom patent application number 0120052.6, filed Aug. 16, 2001, and entitled xe2x80x9cInternal Combustion Engine Coolingxe2x80x9d.
This invention relates to the cooling of internal combustion engines. More particularly the invention relates to a method of cooling an internal combustion engine, to an internal combustion engine assembly including a cooling system, and to an internal combustion engine body incorporating passageways for coolant.
In a conventional internal combustion engine, it is common to provide passageways in the engine body, and to pass coolant through those passageways during operation of the engine to prevent the engine body from overheating. In a typical arrangement, coolant is heated as it passes through the engine body and is then cooled by being passed through a heat exchanger, such as a radiator, before being passed through the engine body again.
Such a cooling system is simple and economical but is also relatively inflexible. In a typical internal combustion engine body, some regions of the engine body are likely to receive relatively large amounts of heat during operation of the engine. The flow rate of the coolant needs to be sufficient to avoid overheating of the engine body in these regions, but may result in other parts of the engine body being cooled to a lower temperature than is necessary or desirable, because of the high flow rate of the coolant, and may also lead to an excessive amount of power being required to circulate the coolant. The situation is further complicated because the various regions of the engine body may receive different amounts of heat according to the condition of the engine and/or the conditions under which it is operating.
It is an object of the invention to provide a method of cooling an internal combustion engine.
It is a further object of the invention to provide an improved internal combustion engine assembly.
It is a still further object of the invention to provide an improved internal combustion engine body.
According to the invention there is provided a method of cooling an internal combustion engine, including the steps of:
(a) providing a circulating primary flow of coolant through passageways in the engine body and a pump, the coolant being heated by the engine body as it flows through the passageways and being cooled after its passage through the engine body,
(b) providing a secondary flow of coolant by removing coolant from the primary flow and injecting it into and mixed with the primary flow at a predetermined location in the engine body,
(c) monitoring a variable that provides an indication of the temperature of the engine body in the region where the secondary flow of coolant mixes with the primary flow of coolant, and
(d) controlling the injection of the secondary flow of coolant into the primary flow in dependence upon the indicated temperature.
The invention further provides an internal combustion engine assembly including:
an engine body and passageways in the engine body defining a flow path for a primary flow of coolant through the engine body,
a pump for generating the primary flow of coolant,
a passage in the engine body leading into the flow path of the primary flow of coolant for enabling a secondary flow of coolant to be injected into and mixed with the primary flow at a predetermined location in the engine body,
a sensing device for sensing a variable that provides an indication of the temperature of the engine body in the region where the secondary flow of coolant mixes with the primary flow of coolant, and
a control system for controlling the injection of the secondary flow of coolant into the primary flow in dependence upon a signal from the sensing device.
The invention still further provides an internal combustion engine body including:
passageways in the engine body defining a flow path for a circulating primary flow of coolant through the engine body,
a passage in the engine body leading into the flow path of the primary flow of coolant for enabling a secondary flow of coolant to be injected into and mixed with the primary flow at a predetermined location in the engine body, and
a temperature sensing device in the region where the secondary flow of coolant mixes with the primary flow of coolant.
By injecting a secondary flow of coolant into the primary flow, it is possible to increase the heat transfer from the engine body to the coolant, and a substantially greater cooling effect in the region of the injection can be obtained by a flow rate of the sum of the primary and secondary flows as compared with the same flow rate provided as a primary flow only. Thus, the power required to circulate the coolant can be reduced, leading to reduced fuel consumption. Furthermore, by assessing the temperature in the region of the enhanced cooling effect and controlling the secondary flow in response to that assessment, it becomes possible not only to achieve greater cooling but also to achieve better control of cooling and, in particular, to provide controlled cooling at different and variable levels in one or more localized regions of the engine body. For example, the secondary flow can be injected into a region of the engine body that otherwise would be particularly hot and can thereby maintain that part of the engine body at a lower temperature, while other parts of the engine body where the cooling from the primary flow is already more than adequate are not cooled any further. By maintaining the various parts of the engine body closer to their ideal temperature, emissions can be reduced and engine component integrity and durability improved. Furthermore, the secondary flow of coolant, and if desired also the primary flow, can be arranged not to be initiated during cold start conditions, thereby saving power and leading to a faster warm-up of the engine and reduction in emissions. Also, the injection of the secondary flow into the primary flow can be employed to reduce any tendency of the coolant to boil in a particular location. Not only may the secondary flow reduce the temperature of the primary flow but it may also, more significantly in terms of avoiding boiling, increase the pressure of the coolant in the region of injection.
Thus, in summary the invention enables much improved control of engine body temperatures while at the same time enabling overall coolant flow rates to be reduced.
The flow velocity of the secondary flow of coolant is preferably substantially greater than the flow velocity of the primary flow of coolant prior to the mixing of the flows, although the volume flow rate (or mass flow rate) of the secondary flow of coolant injected into the primary flow is preferably substantially less than the volume flow rate (or mass flow rate) of the primary flow of coolant into which the secondary flow is injected. Preferably the flow velocity of the secondary flow is at least twice the flow velocity of the primary flow prior to mixing of the flows. Also, preferably the volume flow rate of the secondary flow of coolant injected into the primary flow is less than half the volume flow rate of the primary flow of coolant into which the secondary flow is injected.
The secondary flow of coolant is injected into the primary flow as a jet. It is believed that a factor in enhancing the cooling effect in the region of the injection of the secondary flow is that turbulence is created in the coolant and, as a result, heat transfer between the coolant and the engine body is enhanced. Preferably, the jet is directed through the primary flow onto a surface of the engine body. In that case, the boundary layer of coolant flowing along the passageway is disrupted and either destroyed or significantly reduced in thickness, thereby enhancing the heat transfer between the coolant and the engine body.
The cross-sectional area of the passageway for primary flow and of the passagway for secondary flow will be dependent upon the size of the engine cylinders. In the case of an engine for a road vehicle, the passage for the secondary flow may have a diameter in the range of 2 to 15 mm where the secondary flow of coolant is injected into the primary flow. Preferably, the cross-sectional area of the passageway for the secondary flow of coolant is less than one third of the cross-sectional area of the passageway for the primary flow of coolant where the secondary flow is injected into the primary flow.
The jet of the secondary flow may be directed in an opposing direction of the primary flow of coolant, but it may be preferred that the jet has a direction that has a substantial component aligned with the direction of primary flow of coolant at the predetermined location. For example, the secondary flow may be inclined at an angle on the order of 45xc2x0 to the direction of primary flow. Alternatively, the secondary flow jet may be directed substantially perpendicularly to the direction of primary flow of coolant at the predetermined location.
Although the primary and secondary flows are described as xe2x80x9ccirculatingxe2x80x9d, it should be understood that they do not necessarily operate continuously during operation of the engine. The reference to xe2x80x9ccirculatingxe2x80x9d rather indicates that the flow is around a circuit.
The secondary flow of coolant may be a pulsed flow. The pulsing of the flow is able to generate increased turbulence and increased disruption and penetration of the boundary layer of the primary flow of coolant, as compared to a steady secondary flow of coolant of the same overall flow rate.
The optimum frequency of the pulses will be dependent on the particular physical arrangement, but is preferably in the range of 0.2 to 50 Hz and, for most cases, is in the range of 1 to 10 Hz.
Pulsing of the flow can conveniently be achieved by opening and closing of a control valve in the path of the secondary flow.
While it is possible that in a particular case, the secondary flow of coolant would be injected into the primary flow at only one predetermined location, it is more likely that coolant from the secondary flow is injected into the primary flow at a plurality of predetermined locations in the engine body. For example, it may be desirable to have one injection of secondary flow per cylinder in the engine. Where there is more than one injection of secondary flow, each may be independently controlled or the injections may be controlled together. Thus, the injection of coolant at a first predetermined location may be controlled separately from the injection of coolant at a second predetermined location. It is also possible for a respective variable that provides an indication of temperature to be monitored for each region where the secondary flow of coolant is injected, thereby enabling each injection to be separately controlled relying upon each sensed variable. Thus, a plurality of temperature sensing devices may be provided with each device being located in the region of a respective one of the predetermined locations in the engine body. Providing separate sensing devices and controlling each injection of secondary flow separately improves control but also increases cost.
In a case where the secondary flow of coolant is a pulsed flow and the secondary flow is injected into the primary flow at a plurality of locations, it may be advantageous to arrange for the secondary flow at one location to be taking place when the flow at another location is not, in order that the variation with time in the overall secondary flow rate as a result of the pulsing is reduced or even eliminated. Such an arrangement may be achieved by providing a pump which delivers a pulse of secondary flow to each location.
There are various approaches that may be adopted for obtaining an indication of the temperature in the region of the engine body where the secondary flow of coolant mixes with the primary flow. A simple and direct approach involves measuring a temperature within the engine. That is a simple and direct approach but it may not be possible or economical to locate a temperature sensing device where required, and alternative approaches may therefore be preferred. For example, the composition of the products of combustion, for example, the amount of nitrous oxides, may be used as an indication of engine body temperature. In one approach where temperature is sensed directly, the temperature of part of the engine body immediately adjacent to the mixing of the primary and secondary flows is sensed. Thus, the temperature sensing device is located in the engine body immediately adjacent to the predetermined location. Such an approach has the advantage of providing a direct measurement of the temperature of the part of the engine body most affected by the injection of the secondary flow. In another approach, the temperature of part of the engine body in the vicinity of, but spaced from, the mixing of the primary and secondary flows is sensed. With such an approach, it is still possible to provide an indication of the temperature of the part of the engine body most affected by the injection of the secondary flow because changes in temperature of one part of the engine body will be reflected in changes in temperature in a neighbouring part. This approach may be especially advantageous in a case where the physical arrangement of the engine makes it difficult or impossible to sense the temperature of part of the engine body immediately adjacent to the mixing of the primary and secondary flows.
Preferably, the secondary flow of coolant is generated independently of the primary flow. The secondary flow may be determined by a variable speed pump, the operation of which is controlled in dependence upon the monitored temperature and the pump may be an electric pump. In a case where the secondary flow of coolant is injected into the primary flow at a plurality of locations, it is preferred that a single pump be provided and that, if the injections at the plurality of locations are separately controlled, respective control valves are provided for each of the injections.
It is also preferred that the primary flow of coolant is generated by an electric pump. Although in certain applications it may be desirable, for example for reasons of cost, for the primary flow to be generated by a pump driven mechanically by the engine.
Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which the present invention relates from the subsequent description of the preferred embodiment and the appended claims, taken in conjunction with the accompanying drawings.